Effect of Calcination Temperature on the Activation Performance and Reaction Mechanism of Ce-Mn-Ru/TiO2 Catalysts for Selective Catalytic Reduction of NO with NH3

Striking Improvement of N2 Selectivity in NH3 Oxidation Reaction on Fe2O3-Based Catalysts via SiO2 Doping

The emission of NH3 has been reported to pose a serious threat to both human health and the environment. To efficiently eliminate NH3, catalysts for the selective catalytic oxidation of NH3 (NH3-SCO) have been intensively studied. Fe2O3-based catalysts were found to exhibit superior NH3 oxidation activity; however, the low N2 selectivity made it less attractive in practical applications. In this work, aimed at improving the N2 selectivity on Fe2O3-based catalysts, a simple SiO2 doping strategy was proposed. Although the NH3 oxidation activity showed almost no change on Fe2O3 after SiO2 doping, the N2 selectivity was significantly improved. Systematic characterizations revealed that SiO2 doping could increase the specific surface area of Fe2O3, and a strong interaction of Fe-O-Si was formed in Fe2O3-SiO2 mixed oxide catalysts. Furthermore, abundant Brønsted acid sites were formed on Fe2O3-SiO2 catalysts due to the facile hydrolysis of the Fe-O-Si structure into Si-OH and Fe-OH. Although SiO2 doping was found to weaken the redox ability of Fe2O3, the abundant Brønsted acid sites on Fe2O3-SiO2 catalysts could facilitate NH3 oxidation reaction through an internal SCR (i-SCR) pathway, thus achieving superior N2 selectivity. This work can provide new insights into constructing efficient NH3-SCO catalysts with high N2 selectivity.

Impact of Agricultural Activities on Climate Change: A Review of Greenhouse Gas Emission Patterns in Field Crop Systems

This review paper synthesizes the current understanding of greenhouse gas (GHG) emissions from field cropping systems. It examines the key factors influencing GHG emissions, including crop type, management practices, and soil conditions. The review highlights the variability in GHG emissions across different cropping systems. Conventional tillage systems generally emit higher levels of carbon dioxide (CO2) and nitrous oxide (N2O) than no-till or reduced tillage systems. Crop rotation, cover cropping, and residue management can significantly reduce GHG emissions by improving soil carbon sequestration and reducing nitrogen fertilizer requirements. The paper also discusses the challenges and opportunities for mitigating GHG emissions in field cropping systems. Precision agriculture techniques, such as variable rate application of fertilizers and water, can optimize crop production while minimizing environmental impacts. Agroforestry systems, which integrate trees and crops, offer the potential for carbon sequestration and reducing N2O emissions. This review provides insights into the latest research on GHG emissions from field cropping systems and identifies areas for further study. It emphasizes the importance of adopting sustainable management practices to reduce GHG emissions and enhance the environmental sustainability of agricultural systems.

Low-temperature CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation for selective catalytic reduction of NO using NH3: A structure-activity relationship study

CeCoMnOx spinel-type catalysts for the selective catalytic reduction of NO using NH3 (NH3-SCR) are usually prepared by alkaline co-precipitation. In this paper, a series of CeCoMnOx spinel-type catalysts with different calcination temperatures were prepared by acidic oxalate co-precipitation. The physicochemical structures and NH3-SCR activities of the CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation and conventional ammonia co-precipitation were systematically compared. The results show that the CeCoMnOx spinel-type catalysts prepared by the oxalate precipitation method (CeCoMnOx-C) have larger specific surface area, more mesopores and surface active sites, stronger redox properties and adsorption activation properties than those prepared by the traditional ammonia co-precipitation method at 400 °C (CeCoMnOx-N-400), and thus CeCoMnOx-C have better low-temperature NH3-SCR performance. At the same calcination temperature of 400 °C, the NO conversion of CeCoMnOx-C-400 exceeds 89 % and approaches 100 % within the reaction temperature of 100-125 °C, which is 14.8 %-2.5 % higher than that of CeCoMnOx-N-400 at 100-125 °C. In addition, the enhanced redox and acid cycle matching mechanisms on the CeCoMnOx-C surface, as well as the enhanced monoadsorption Eley-Rideal (E-R) and double adsorption Langmuir-Hinshelwood (L-H) reaction mechanisms, are also derived from XPS and in situ DRIFTS characterization.

A novel high activity MnXFe3-XO4 spinel catalyst for selective catalytic reduction of NO using NH3 prepared by a short process from natural minerals for low-temperature sintering flue gas: Effect of X value on catalytic mechanism

The process of smelting and purifying the catalyst precursor salt from minerals is extremely complex, which directly leads to high catalyst costs and serious secondary pollution. In order to achieve energy saving and emission reduction in the catalyst preparation process, in-situ synthesis of catalyst materials from natural minerals is a new research direction. In this study, we firstly explored the optimal X value of MnXFe3-XO4 for the NH3 selective catalytic reduction of NO (NH3-SCR) reaction, i.e., the Mn, Fe ratio, and then prepared a novel highly active mineral-based pure phase MnXFe3-XO4 spinel NH3-SCR catalyst by natural ferromanganese ore fines with iron-red fines (Fe2O3) allotment through in situ solid-phase synthesis and magnetic separation methods according to this ratio. The results show that the X value of 1.5 (Mn1.5Fe1.5O4) is the best for NH3-SCR reaction. Mn1.5Fe1.5O4 nano-particles (201 nm) has nearly 100 % NO conversion (with 5 % H2O(g)) at 125-300 °C. The combination of characterizations and density functional theory (DFT) calculation shows that the catalytic process of Eley-Rideal (E-R) dehydrogenation is enhanced at both the active site Mn site and Fe site, which is a key factor in the acceleration of the NH3-SCR reaction with increasing X value at the MnXFe3-XO4 surface.

Temperature-Dependent Structures of Single-Atom Catalysts

Single-atom catalysts (SACs) have the unique coordination environment and electronic structure due to the quantum size effect, which plays an essential role in facilitating catalytic reactions. However, due to the limited understanding of the formation mechanism of single atoms, achieving the modulation of the local atomic structure of SACs is still difficult and challenging. Herein, we have prepared a series of Ni SACs loaded on nitrogen-doped carbon substrates with different parameters using a dissolution-and-carbonization method to systematically investigate the effect of temperature on the structure of the SACs. The results of characterization and electrochemical measurements are analyzed to reveal the uniform law between temperature and the metal loading, bond length, coordination number, valence state and CO2 reduction performance, showing the feasibility of controlling the structure of SACs through temperature to regulate the catalytic performance. This is important for the understanding of catalytic reaction mechanisms and the design of efficient catalysts.

In Situ Construction of Manganese Oxide Photothermocatalysts for the Deep Removal of Toluene by Highly Utilizing Sunlight Energy

The alternative use of electric energy by renewable energy to supply power for catalytic oxidation of pollutants is a sustainable technology, requiring a competent catalyst to realize efficient utilization of light and drive the catalytic reaction. Herein, in situ-synthesized manganese oxide heterostructure composites are developed through solvothermal reduction and subsequent calcination of amorphous manganese oxide (AMO). 95% of toluene conversion and 80% of CO₂ mineralization were achieved over amorphous manganese oxide calcined at 250 °C (AMO-250) under light irradiation, and catalyst stability was maintained for at least 40 h. Highly utilization of light energy, uniformly dispersed nanoparticles, large specific surface area, improved metal reducibility, and oxygen desorption and migration ability at low temperature contribute to the good catalytic oxidation activity of AMO-250. Light activated more lattice oxygen to participate in the reaction via the Mars-van Krevelen (MvK) mechanism, and traditional e^--h⁺ photocatalytic behavior exists over the AMO-250 heterostructure composite as an auxiliary degradation path. The reaction pathways of photothermocatalysis and thermocatalysis are close, except for the emergence of different copolymers, where light enhances the deep conversion of intermediates. A proof-of-concept study under natural sunlight has confirmed the feasibility of practical application in the photothermocatalytic degradation of pollutants.

Ultrasonication-Assisted Preparation of a Mn-Based Blast Furnace Slag Catalyst: Effects on the Low-Temperature Selective Catalytic Reduction Denitration Process

Reducing costs and improving performance have always been hotspots in the field of catalyst research. In order to control the NO x in the low-temperature flue gas of nonpower industries, this paper studies the denitration performance of the ultrasonication-assisted preparation of Mn-based blast furnace slag selective catalytic reduction (SCR) low-temperature denitration catalysts. The catalyst was characterized by FT-IR, XRD, and SEM. The study found that ultrasound assistance can make the active components on the catalyst surface more uniformly dispersed and improve the catalytic activity of the catalyst. Under conditions of 80 W ultrasonic power and 20 min ultrasonic time, the denitration performance of the Mn-based blast furnace slag catalyst is optimal, and the NO removal rate is 2.5 times that of the unsonicated catalyst. This work clarified the mechanism of the effect of ultrasonic assistance on the Mn-based blast furnace slag catalyst and at the same time realized the utilization of solid waste resources and air pollution control.

Synthesis and Characterization of Titanium Dioxide Hollow Nanofiber for Photocatalytic Degradation of Methylene Blue Dye

Environmental crisis and water contamination have led to worldwide exploration for advanced technologies for wastewater treatment, and one of them is photocatalytic degradation. A one-dimensional hollow nanofiber with enhanced photocatalytic properties is considered a promising material to be applied in the field. Therefore, we synthesized titanium dioxide hollow nanofibers (THNF) with extended surface area, light-harvesting properties and an anatase–rutile heterojunction via a template synthesis method and followed by a calcination process. The effect of calcination temperature on the formation and properties of THNF were determined and the possible mechanism of THNF formation was proposed. THNF nanofibers produced at 600 °C consisted of a mixture of 24.2% anatase and 75.8% rutile, with a specific surface area of 81.2776 m²/g. The hollow nanofibers also outperformed the other catalysts in terms of photocatalytic degradation of MB dye, at 85.5%. The optimum catalyst loading, dye concentration, pH, and H₂O₂ concentration were determined at 0.75 g/L, 10 ppm, pH 11, and 10 mM, respectively. The highest degradation of methylene blue dye achieved was 95.2% after 4 h of UV irradiation.